In one technology, as a method for detecting an abnormality of a resolver to be used for detecting a rotating angle of an electric motor or the like, for example, there is a technique disclosed in Patent Literature 1. In this technique, in synchronization with a maximum value or a minimum value of an excitation signal of the resolver, each resolver output signal is sampled, and when an offset of the sampled value falls out of a given range near 0, it is determined that an abnormality occurs at the resolver.
In addition, as another method for detecting the abnormality of the resolver, for example, there is a technique disclosed in Patent Literature 2. In this technique, different values are set to the respective voltage transformation ratios between the excitation coil and the respective three resolver coils, and when three rotor electrical angles (operation electrical angles) operated from the three-phase resolver signal indicate different values from one another, it is determined that a short-circuit abnormality occurs at the resolver.